Method and apparatus for desalination

Abstract

A method and apparatus for purifying water are provided. A feed water such as seawater can be fed to a filter such as a nanofiltration membrane to produce a permeate that can, in turn, be fed to an electrodeionization system to produce fresh water.

1. A method of reducing total dissolved solids in seawater comprising:
 reducing a concentration of dissolved solids in the seawater in a nanofiltration device to produce a first partially treated water; 
 reducing a concentration of dissolved solids in the first partially treated water in an electrodialysis device to produce a second partially treated water; and 
 reducing a concentration of dissolved solids in the second partially treated water in an electrodeionization device to produce treated water having less than about 1,000 ppm total dissolved solids and a boron content of less than about 0.5 ppm, 
 wherein energy consumption to produce the treated water through the nanofiltration device, the electrodialysis device, and the electrodeionization device is less than about 7 kwh/kgal. 
 
     
     
       2. The method of  claim 1  wherein the nanofiltration device is operated at an upstream pressure of less than about 600 psi. 
     
     
       3. The method of  claim 1  wherein the treated water comprises less than about 500 ppm total dissolved solids. 
     
     
       4. The method of  claim 1 , further comprising mixing a concentrate stream from the electrodeionization device with the seawater upstream of the nanofiltration device. 
     
     
       5. The method of  claim 1 , wherein reducing the concentration of dissolved solids from the first partially treated water comprises producing the second partially treated water from an electrodialysis device having monovalent selective membranes. 
     
     
       6. The method of  claim 1 , wherein reducing the concentration of dissolved solids in the seawater in a nanofiltration device comprises reducing a concentration of monovalent species in the seawater stream to produce the first partially treated water product. 
     
     
       7. The method of  claim 1 , wherein the treated water has more than about 230 ppm total dissolved solids.